The present invention relates to a head substrate provided with a driver IC which selectively drives a plurality of driving elements.
As an example of an electronic device, a thermal printer is known. The thermal printer includes a thermal head where heater elements are disposed in a straight line. The heater elements disposed on the thermal head are selectively heated by being energized. The thermal energy corresponds selectively to a color fixing agent included in a thermal paper, so that a variety of information is printed on the thermal paper. The printing scheme is known as thermal coloring scheme.
Such thermal head includes a long rectangular thermal head substrate (substrate), plural heater elements (heating resistor) that are disposed on one end of a longitudinal side of the substrate along the longitudinal side, and driver ICs that are disposed in parallel to the plural heater elements and selectively drives the heater elements. On the thermal head substrate, an output signal wiring pattern is formed between the heater elements and the driver ICs so as to connect each other, and an input signal wiring pattern for the driver ICs is formed on a side facing the heater elements with the driver ICs being interposed therebetween.
The heater element is electrically conducted to a separate electrode and a common electrode, and the separate electrode is connected to an output pad of the driver IC via the output signal wiring pattern by using a wire bonding, etc. The driver IC turns on a predetermined output pad according to print data inputted via the input signal wiring pattern. A current flows between the separate electrode and the common electrode that correspond to the turned-on output pad, and thus a predetermined heater element is driven (for example, see Patent Document 1). Further, the driver IC that drives the predetermined heater element includes a control circuit including shift registers and latch circuits as a single IC chip (for example, see Patent Document 2). Further, it is also disclosed that the input signal wiring pattern, which can be simplified and where a width of the pattern which can be widened, is also provided on a mounting region of the driver IC (for example, see Patent Document 3).    Patent Document 1: Japanese Patent Publication No. 07-081114A    Patent Document 2: Japanese Patent Publication No. 2001-301211A    Patent Document 3: Japanese Patent Publication No. 05-063022A
The driver IC mounted on the above-mentioned thermal head substrate, for example, lets a current flow into the separate electrodes that correspond to the heater elements for 128 bits per one driver IC. For example, when the thermal head substrate includes 512 heater elements, four driver ICs are arranged. Therefore, 128×4 separate electrode patterns are formed on the thermal head substrate, and the common electrode pattern or the input signal wiring pattern including a ground line, a clock signal line, a logic power line, a latch signal line, and a strobe signal line is formed. For this reason, a layout of the pattern is complicated, and an area for forming the pattern is increased. As a result, an area of the thermal head substrate is increased, and thus the physical size of the thermal head is also increased. That is, it is difficult to achieve miniaturization of the thermal head and a cost reduction corresponding thereto. Patent Document 3 provides a countermeasure to this difficulty. However, in this case, the clock signal line and the latch signal line are disposed on the mounting region of the driver IC, where the high-frequency clock signal noise affects other portions, especially output lines of head driving signals, which causes an error.